In the forthcoming evolution of mobile cellular standards like GSM and WCDMA, new transmission techniques like OFDM will be used. Furthermore, in order to have a smooth migration from existing cellular systems to high capacity high data rate systems in existing radio spectrum, new systems must be able to operate in a flexible bandwidth. A proposal for such a new flexible cellular system is 3G Long Term Evolution (3G LTE) that can be seen as an evolution of the 3G WCDMA standard. This system will use OFDM as multiple access technique (called OFDMA) in the downlink and will be able to operate on bandwidths ranging from 1.25 MHz to 20 MHz. Another important aspect of LTE is the mobility function, hence synchronization symbols and cell search procedures are of major importance in order for a terminal operating in the system to detect and synchronize with other cells.
For mobility reasons the terminal needs to read system information from cells, e.g. serving cell and neighbouring cells, prior to handover, in order to collect necessary information as to be able to connect to that other cell. The problem is that the neighbouring cell typically is weaker than the serving cell and hence the detection of broadcast information needs to be done at signal-to-interference ratios (SIRs) below 0 dB. Furthermore, in LTE, reference symbols (RS) are sparse, which makes channel estimation, especially at low SIR, a non-trivial task. This in turn causes the detection of broadcast system information, e.g. the primary broadcast channel (P-BCH), to have quite low performance.
Therefore there is a need for method and apparatus for improving the channel estimates in systems like the LTE to enable acquisition of system information from cells.